1. Field of the Invention
This invention relates to a bicycle hub unit which is to be attached to the rear wheel of a bicycle and which enables its cone to be mounted reliably on a hub shell thereof so as to minimize wobbling of the cone relative to the hub shell when in use.
2. Description of the Related Art
The invention is an improvement of a conventional bicycle hub unit, as shown in FIGS. 1 and 2, which is to be attached to the rear wheel of a bicycle. The bicycle hub unit includes a hub shell 1 which has an axial bore 11 that has a first axial end portion and a second axial end portion opposite to the first axial end portion. The hub shell 1 is supported rotatably on a hub shaft (not shown) that is mounted securely on the axle of the rear wheel of the bicycle. The hub shell 1 further has an annular series of external splines 12 which are formed at an outer end surface of the second axial end portion of the axial bore 11 of the hub shell 1, and an annular shoulder 13 (see FIG. 2) which is formed on an inner peripheral surface of the hub shell 1 near the first axial end portion of the axial bore 11. A hollow bolt 2 extends through the axial bore 11 of the hub shell 1 and is sleeved on the hub shaft. The bolt 2 has an externally threaded tip portion 21 which extends out of the second axial end portion of the axial bore 11, and a head portion 22 which bears against the shoulder 13. A first bearing 3 is disposed within the first axial end portion of the axial bore 11 of the hub shell 1. A cone 5 includes a head portion which is sleeved on the external splines 12 of the hub shell 1 and which has an annular series of internal splines 51 (see FIG. 2) meshing with the external splines 12 of the hub shell 1. Accordingly, when assembled, the hub shell 1 is co-rotatable with the cone 5. The cone 5 further includes an externally threaded tip portion 52, two pairs of ratchet pawls 53 supported on an outer circumference of the cone 5, and an internally threaded portion 54 (see FIG. 2) formed on the inner circumference of the cone 5 and connected threadably to the externally threaded tip portion 21 of the bolt 2 so as to fix the cone 5 to the hub shell 1.
A sprocket carrier 6 is supported around the cone 5 and has an annular series of ratchet teeth 61 formed on an inner circumference thereof.
A waterproof ring 4 is disposed on one end of the sprocket carrier 6 around the second axial end portion of the axial bore 11, and abuts against the hub shell 1.
The ratchet pawls 53 are spring-biased and engage operably the ratchet teeth 61 such that the sprocket carrier 6 is co-rotatable with the cone 5 in a forward running direction for torque transmission, and is freely rotatable relative to the cone 5 in the opposite direction to enable inertial running of the bicycle. Thus, the sprocket carrier 6 can rotate relative to the cone 5 only in one direction.
A second bearing 7 is disposed within the sprocket carrier 6 and has an internally threaded portion 71 which is connected threadably to the externally threaded tip portion 52 of the cone 5.
A plurality of diametrically different sprockets 8, as shown in FIG. 3, are supported on the sprocket carrier 6 for co-rotation therewith.
In general, the hub shell 1 is made of a light metal, such as an aluminium alloy, which is relatively weak in strength. However, when the conventional bicycle hub unit is in use, the external and internal splines 12, 51 of the hub shell 1 and the cone 5 have to bear a relatively large force. The force is applied only on one side of the sprocket carrier 6 and the cone 5 so that only a few of the external and internal splines 12, 51 at the force-applied side of the cone 5 receive the force.
As a result, the cone 5 may wobble easily relative to the hub shell 1 when the bicycle hub unit is in use. To make matters worse, the farther the external and internal splines 12, 51 are located from the center of gravity of the hub shell 1, the more violent the cone 5 wobbles relative to the hub shell 1.
Further, because the hollow bolt 2 is relatively long, it increases the weight of the bicycle hub unit and is easily bent due to long-term use. Thus, the bent bolt 2 may result in deviation of the internal splines 51 of the cone 5 from the external splines 12 of the hub shell 1. As a result, the bolt 2 may increase the wobbling of the cone 5 relative to the hub shell 1.